The Registry Mechanic trial software a user claims showed him fake errors to convince him to pay for a full $29.99 version.

Security firms often warn users about "scareware": malicious software that performs fake antivirus scans and then demands the user pay for a cleanup. Now a lawsuit claims that the world's top antivirus firm, Symantec, is itself a scareware scammer.

James Gross, a resident of Washington State, filed what he intends to be a class action lawsuit against Symantec in a Northern District California court Tuesday. Gross claims that Symantec defrauds consumers by running fake scans on their machines, with results designed to bully users into upgrading to a paid version of the company's software.

"The Scareware does not conduct any actual diagnostic testing on the computer," the complaint reads.

Instead, Symantec intentionally designed its Scareware to invariably report, in an extremely ominous manner, that harmful errors, privacy risks, and other computer problems exist on the user’s PC, regardless of the real condition of the consumer’s computer. Furthermore, the scareware does not, and cannot, provide the benefits promised by Symantec. Accordingly, consumers duped into purchasing software that does not function as advertised, and in fact, has very little (if any) utility.

In the complaint, Gross goes on to describe his experience of running a Symantec scan with the company's Registry Mechanic software he found on Symantec's PCTools.com. After the scan's results showed his computer contained "high priority" errors and its "system health" was "low," he paid $29.99 to resolve the problems. Gross says he later hired computer forensics experts who found that Symantec's scan always produced those disturbing results, and that the errors it found were "not credible threats to a computer's functionality."

When I reached out to Symantec, the company responded in a statement that it "does not believe the lawsuit has merit and will vigorously defend the case."

"The Norton and PC Tools solutions at issue are designed to improve the system performance of our customers' devices in terms of speed, maintain the health of their machines, and protect our customers' information," the statement continues. "The optimization and privacy functions of these solutions fix registry errors, wipe computer usage, and shred deleted items. Some include additional functionality such as recovery tools to restore lost items. Several independent third parties have tested and reviewed these products very favorably, verifying the effectiveness of their functionality."

Gross's most extreme claim, that Symantec's software has no purpose, will no doubt be difficult to defend in court. And when I tested Registry Mechanic on my machine, it didn't ask me to pay for the full version. Despite finding many so-called "high priority" issues, the software resolved them for free.

But Symantec certainly has a history of exaggerating threats to boost sales. In one message that Symantec showed in 2010 to users whose antivirus subscriptions expired, it warned that "Any second now a virus might infect your computer, malicious malware might be installed, or your identity may be stolen. Maybe things will be OK for a while longer. Then again, maybe cybercriminals are about to clean out your bank account. The choice is yours: Protect yourself now, or beg for mercy."

Gross's lawsuit, of course, goes beyond alleging mere fearmongering to actual fraud. And as the trial goes forward, it may be Symantec's engineers, not just its marketing department, that have to answer his accusations.